BEIJING -- The average density of PM 2.5, fine particulate matter that causes smog, in the Beijing-Tianjin-Hebei region dropped by 26.5 micrograms per cubic meter, or 30 percent, from 2013 to 2016, according to satellite data released by the Chinese Academy of Sciences (CAS) on Wednesday.

The CAS, at a press conference in Beijing, disclosed findings of its researchers on the cause, early warning, forecasting and surveillance of smog as well as clean coal technology.

According to remote-sensing satellite data, despite the overall lowering of smog density in the region, air quality worsened in Beijing during the winter.

The average density of PM 2.5 in Beijing during winter mounted from 70 micrograms per cubic meter in 2014 to 89 micrograms per cubic meter in 2015, and to 110 micrograms per cubic meter in 2016.

Gu Xingfa, head of the Institute of Remote Sensing and Digital Earth of the CAS, said the remote sensing satellite data proved that Beijing did make headway in smog control, but public complaints about worsening pollution since the winter of 2016 were also valid.